#include <iostream>
using namespace std;
long long func(int x)
{
    if (x == 0)
        return 0;
    long long a = 0, b = 1;
    long long c = 1;
    for (int i = 1; i < x; i++)
    {
        c = (long long)a + b;
        a = b;
        b = c;
    }
    return c;
}
int main()
{
    int x;
    cin >> x;
    printf("%.2lf", (double)func(x));
}